For those that pushed the Public Mobile $40/4GB deal hard to friends and family, they should be rewarded for their efforts.
For those that managed to get enough referrals to cover their plan--and some more--those extra referral credits should NOT go to waste. They should stay in the account balance for purchasing add-ons or paying for a more expensive or larger data plan in the future.
Public Mobile referral credits should remain in a balance and not waste away if you've put in the hard work to bring people to this network and gain more than enough credits to pay for your bill.